There are several techniques for welding cast iron.
Cast iron is an iron alloy which contains a significant amount of carbon and is known for its brittleness. Gray cast iron is the most common type. The carbon content is typically 2 to 4 percent, roughly ten times more than other alloys, including wrought iron or steel. The carbon in the molten iron forms graphite flakes which causes the alloy to be brittle. Due to its brittleness, cast iron objects or parts can be difficult to weld. There are several methods that, if employed correctly, make the weld much easier. Does this Spark an idea?
A Clean Surface
Thoroughly clean the surface or crack to be welded. This provides for a better weld and helps prevent cracks.
Preheating Technique
This technique involves preheating the object to between 500 and 1,200 degrees Fahrenheit. Avoid heating the metal over 1,400 degrees Fahrenheit as it becomes molten at this temperature. Weld the cast iron using a low current. Monitor the width of the welds--they should not exceed an inch in length. Wide welds can lead to cracks. After welding, allow it to cool undisturbed and gradually. The object can be buried in sand or covered in an insulation blanket to facilitate cooling.
Without Preheating
Welding without preheating requires control over the welding gun and small welds, no more than one inch in width. Welds should be allowed to cool gradually. Once cooled, use the opposite end of the flat side of a hammer to chip off and work the welds until the surface is smooth. This process is known as peening. Welding without preheating is recommended for domestic purposes.
Studding Technique
The studding technique requires a high level of skill. First, drill and tap holes in the surface to be welded. Next, insert steel studs and weld them in. The studs help cover the area of the crack to be repaired. The weld serves to make a reinforcement over the crack.
Dealing With Crack Formations
Due to cast iron's brittleness, cracks can appear near welds even when the proper procedure has been followed. If a water tight seal is necessary, use a sealing compound. The preheating technique can also be used to seal cracks.
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